Lysosomal cystine export regulates mTORC1 signaling to guide kidney epithelial cell fate specialization (Microarray)

Differentiation is critical for epithelial cell fate decisions, but the signals involved remain unclear. The kidney proximal tubule (PT) cells reabsorb disulphide-rich proteins through endocytosis, generating cystine via lysosomal proteolysis. Here we report that defective cystine mobilization from lysosomes through cystinosin (CTNS), which is mutated in cystinosis, diverts PT cells towards growth and proliferation, disrupting their functions. Mechanistically, lysosomal cystine storage stimulates Ragulator-Rag GTPase-dependent recruitment of mechanistic target of Rapamycin complex 1 (mTORC1) and its constitutive activation. Re-introduction of CTNS restores nutrient-dependent regulation of mTORC1 in knockout cells, whereas cell-permeant analogues of L-cystine, accumulating within lysosomes, render wild-type cells resistant to nutrient withdrawal. Therapeutic mTORC1 inhibition corrects lysosome and differentiation downstream of cystine storage, and phenotypes in a zebrafish model of cystinosis. Thus, cystine serves as a lysosomal signal that tailors mTORC1 signaling and metabolism to direct epithelial cell fate decisions. These results identify mechanisms and therapeutic targets for dysregulated homeostasis in cystinosis. Comparative gene expression profiling analysis of RNA-seq data on kidney cortex from CTNS KO Mouse and Rat model vs WT control细胞分化对于上皮细胞命运决定至关重要，但其涉及的信号通路仍未明确。肾脏近端小管（PT）细胞通过胞吞作用重吸收富含二硫键的蛋白质，经溶酶体蛋白水解过程生成胱氨酸。本研究发现，因胱氨酸病发生突变的胱氨酸转运蛋白（cystinosin, CTNS）功能缺陷，会阻碍溶酶体中胱氨酸的动员，使PT细胞转向生长与增殖状态，进而破坏其正常生理功能。机制层面，溶酶体内胱氨酸蓄积会触发依赖Ragulator-Rag GTP酶的雷帕霉素靶蛋白复合物1（mechanistic target of Rapamycin complex 1, mTORC1）招募过程，使其发生持续性活化。重新导入CTNS可恢复CTNS敲除细胞中mTORC1的营养依赖性调控；而可在溶酶体内蓄积的L-胱氨酸细胞通透性类似物，则会使野生型细胞对营养剥夺产生抵抗。通过治疗性手段抑制mTORC1，可纠正胱氨酸蓄积下游的溶酶体功能异常与分化紊乱，并改善胱氨酸病斑马鱼模型的表型。综上，胱氨酸可作为一种溶酶体信号，通过调控mTORC1信号通路与代谢状态，指导上皮细胞的命运决定。本研究结果阐明了胱氨酸病中稳态失衡的潜在机制与治疗靶点。本研究针对CTNS敲除小鼠、大鼠模型及野生型对照组的肾脏皮质组织，开展了RNA测序（RNA-seq）数据的比较基因表达谱分析。